1. Field of the Invention
The present invention relates to packet processing devices and more particularly to a packet processing device that processes packets with firmware of a central processing unit (CPU).
2. Description of the Related Art
Mobile communication devices such as cellular phones are increasingly used in recent years, which leads to an explosive growth of packet traffic flowing over wireless networks. In such circumstances, CPUs employed for packet processing are under a heavy load and thus experience firmware hang-up (freezing) problems more and more often, resulting in degraded quality of communication service. For this reason, the packet processor in a radio network controller (RNC, an upper-level station that manages base stations) is designed to alleviate the CPU workload by limiting the number of packets to be processed in each unit time, depending on the length of received packets.
For example, the Japanese Patent Application Publication No. 2004-007256, paragraphs Nos. 0020 to 0035 and FIG. 1 proposes a technique of controlling packet transmission based on packet lengths. According to this technique, a packet routing device calculates a suspend time from the lengths of received packets and sends back a suspend packet containing the calculated suspend time, so that the sender will suspend transmission of next packets for the specified suspend time.
Such packet processing devices process packets whose length varies from packet to packet. Think of an incoming packet flow with a specific traffic bandwidth. The number of packets depends, in general, on the packet length. To be more specific, the traffic may actually be a small number of long packets. Or it many be a large number of short packets. In the latter case, the packet processing device has to process packet headers more often than in the former case. This results in an excessive overhead of packet processing, which consumes more CPU-time resources than in the case of long packets, consequently affecting control tasks for other subsystems in the device.
As can be seen from the above discussion, an increase in the number of incoming short packets, or in the number of connection paths established at the packet processing device, will raise the CPU-time consumption. This brings more chances for hang-up of packet processing, as well as causing adverse effect on other control tasks. The conventional technique of reducing CPU load based only on the packet length is not effective enough to solve, or even alleviate, the problem.